Synthesis of poly(adenosine diphospho ribose) (poly(ADPR)) will be compared in cells derived from normal humans and from patients with genetic disorders of DNA repair. These different cell types will be analyzed in different growth stages, before and after treatment with DNA damaging agents to determine whether they show differences in their rates of poly(ADPR) synthesis, their concentrations of the enzyme substrate, NAD or their acceptors for poly(ADP Ribosylation). By comparing these aspects of poly(ADPR) synthesis in the different cell types we will determine whether defects in poly(ADPR) synthesis are etiologically involved in disorders of DNA repair such as Xeroderma pigmentosum, Fanconi's anemia, Ataxia telangiectasia, and Bloom's syndrome.